I've done metric centuries on my affinity and I can say that it all depends on the build you will do, mine is set up for comfort no tarck nonsense (track drops, track pedals, anchor wheels, ****ty tires). Does it demand more then a relaxed geo? Sure, but I do not find it unconfortable.
re sloping top tube: it's a track geometry as any other track bike, people usually call it a faux pro (instead of 650 forks), the top tube doesn't change the bike geo, it just means that there will be less seatpost apparent.